The present invention relates to an air intake, and to a flying device, particularly a missile, equipped with such an air intake.
It is known that an air intake which is mounted on a flying device such as a missile for example, is intended to convey air, in flight, from outside the flying device to internal means, generally means intended to propel said flying device, such as a ramjet combustion chamber for example. Such air intakes are described in numerous documents, particularly in patents FR-2 755 182, DE-30 03 004 and EP-0 474 594, and generally comprise an elongate duct of roughly rectangular cross section.
In the case of a ramjet, it is known that the quality of operation of the ramjet and its efficiency depend to a large extent on the magnitude of the ingested air flow rate, that is to say on the flow rate of air conveyed by the air intake or intakes into the ramjet combustion chamber, in which a mixture of air and fuel is burnt. The ingested air flow rate of course depends on the planned cross-sectional area of the air intake (or air intakes). Of course, the larger this area, the greater the flow rate.
However, it is not desirable to provide a flying device with excessively large air intake cross-sectional areas, particularly for size, mass and aerodynamic reasons.
In addition, particularly when intended to supply air to propulsion means of the ramjet type, an air intake has to have good performance, in terms of efficiency and flow rate, in a broad flight envelope, and be suited to the Mach number and the flight altitude.
What happens is that low-altitude flights can be envisaged only at modest Mach numbers, for material temperature withstand reasons, whereas at high altitude, the Mach number needs to be much higher so as, because of the rarefaction of the air, to make it possible to maintain sufficient dynamic pressure to provide the flying device with lift and/or acceleration.
Hence, to obtain high thrust over the entire trajectory of the aerial vehicle, both at low altitude and at high altitude, it is necessary to provide the propulsion means with a very variable flow rate of combustion air.
To achieve this objective, one known solution is to vary the inlet cross section of the air intake. Various air intakes with variable air inlet cross sections are known. In particular, patent EP-0 646 525 discloses a variable-geometry two-dimensional supersonic and hypersonic air inlet for the combustion air of an aircraft engine. This air inlet is placed under the wing structure or the fuselage of the aircraft, and comprises two main flaps arranged facing each other, of which the internal walls, facing each other, are arranged as compression ramps. Each of said flaps can move about an axis of pivoting situated near a wall of the air inlet which continues the relevant main flap backward. In addition, a ramp, which can move about an axis of pivoting parallel to the axes of pivoting of the main flaps, and situated near its leading edge, is arranged upstream of the main flap closest to the wing structure or fuselage. This upstream ramp together with said main flap delimits a boundary layer bleed of variable cross section.
Such an air inlet has the advantage that the orientable upstream ramp diverts the air flow toward the central plane of the air inlet and makes it possible to form, and to maintain, right up to the superramjet operating phase, a boundary layer bleed of variable cross section of a satisfactory size.
However, since the main flaps and the upstream ramp, and the actuating means, are arranged inside the air inlet, they, of necessity, disrupt the flow. In addition, as this known solution envisages a high number of different elements (main flaps, ramp, etc.), it is complicated, bulky and expensive. Furthermore, because of the high pressure generated by the air at high flow rate which enters the air inlet and because of the means of attachment provided, comprising just two attachment regions (pivot and actuator) for each of these pivoting elements, there is doubt over the stability of these elements throughout the flight envelope.
It is an object of the present invention to overcome these drawbacks. The invention relates to an air intake which is simple, efficient, and low-cost, allowing air to be conveyed at a variable flow rate.
To this end, according to the invention, said air intake of the type comprising an elongate duct which has an air inlet end and an air outlet end and which has at least one roughly planar face, is notable in that it further comprises:
a moving ramp comprising an elongate structure which is, at least in part, roughly planar face which is arranged on the outside on said planar of the duct, and which is able to be moved in translation over said planar face along said duct and be brought into one of at least two stable positions in which it is stationary with respect to said duct:
a retracted position, in which it is set back from said air inlet end, on said planar face of the duct; and
a deployed position in which, while being partially arranged on said planar face, it protrudes from the duct at its air inlet end; and
operable actuating means for moving said moving ramp and bringing it into one of said stable positions.
Thus, by virtue of the invention, for the same condition of use of the air intake, it is possible to obtain two different air flow rates, depending on the position (retracted or deployed) into which the moving ramp is brought. Specifically:
in the retracted position, the ramp is set back from the air inlet end of the duct and therefore has no influence on the air entering the air intake, which means that the air flow rate is defined by the (constant) cross section of said air inlet end, and, of course, by the conditions of use (air speed, etc.);
whereas, in the deployed position, the ramp protrudes beyond the duct at its (air) inlet end, which means that it acts on the air upstream of said inlet end and guides some of this air toward said inlet end in such a way as to increase the amount of air entering the air intake, and the pressure, which has the effect of increasing the air flow rate (by comparison with the flow rate there is in the retracted position).
In consequence, depending on the air flow rate needed, the ramp is brought into one or other of said stable positions.
In addition, since the ramp is arranged on the external face of said planar face of the duct, it does not disrupt the air flow inside the air intake.
Furthermore, as will be seen in greater detail hereinbelow, the present invention also has the following advantages:
it is compact;
the ramp is moved precisely; and
the ramp is very stable in its retracted and deployed positions.
It will be noted that, in the context of the present invention, it is of course conceivable to provide more than two stable positions by providing one or more (deployed) stable positions which are intermediate between the retracted position and the fully deployed position.
In a preferred embodiment, said actuating means comprise:
a system involving collaborating rail and slide, which is intended to secure the ramp to said duct, while at the same time allowing said ramp to move; and
means of moving and fixing said moving ramp.
This makes it possible to obtain (retracted and deployed) positions which are very stable and controlled and also stable movement of the ramp, particularly by comparison with the aforementioned customary solution (patent EP-0 646 525 for example) in which the elements (flap, ramp) acting on the air are pivotable (rather than movable in translation) and are held generally at just two points, at a pivot and at an actuator.
Furthermore, advantageously, said means of moving and fixing the moving ramp comprise:
a geared motor unit, of conventional type, which can be operated electrically, and is able to move the moving ramp with the aid of an assembly formed of a rack and of a pinion, so as to convey it into one of said stable positions, and able to fix said ramp with respect to said duct in one of said stable positions; and
operating means for electrically operating said geared motor unit.
This embodiment has, in particular, the following advantages:
absence of maintenance (no operations such as changing seals or performing major periodic inspections, for example, as is the case with a hydraulic system);
long life; and
possibility of multiple uses (unlike a pyrotechnic system for example).
In this case, as a preference, said operating means for electrically operating said geared motor unit are connected by an electric connection to the latter and are arranged some distance from said geared motor unit. As a consequence, only the geared motor unit which needs to be arranged near the ramp in order to be able to operate and act as envisaged is potentially bulky, it being possible for the operating means for their part to be arranged at a point where they cause no impediment.
Furthermore, advantageously, said ramp comprises a planar first part intended to be arranged on said planar face of the duct and at least one second part which is connected to said planar first part roughly at right angles and which has at least one through-opening which, when the ramp is in said deployed position, is situated beyond the duct at the air inlet end. This opening allows a boundary layer of air to be removed.
The present invention relates also to a flying device, particularly a missile, comprising at least one air intake for conveying air from the outside into said flying device, particularly to propulsion means such as a ramjet for example.
According to the invention, said flying device is notable in that said air intake is of the aforementioned type.